TL;DR:
1. Ideas are super easy. You just need to realize they don't need to be ground-breaking. The simpler the better.
2. None of us WANT to work more after 9-5 work, especially those of us with families, kids, other non-work commitments. So we need good HABITS and lots of DISCIPLINE to FORCE us to work when we don't want to. Motivation is overrated.

1. This always seems to be the easiest part for me. I never understand people who say 'i just don't have any ideas/problems to work on.' WHAT?! There are literally 100s of tasks you do everyday, that you can turn into a small app to help others do that thing, or take the pain points out of doing that thing.

You don't NEED to care about the task that much, just care enough to spend some time building an app to help others do that thing.

Ideas don't have to be 'earth-shattering', or 'game-changing', or 'industry-changing'. They just need to be something that will help someone else do something. It's insanely simple to 'come up with ideas'. They won't all be MILLION DOLLAR ideas, but ideas are the simple part, imho.

Also, YOU don't have to want to pay for your idea. Most times you never would. Why? Because for whatever reason, you've already found the solution to the problem of your idea? I would never pay for someone to teach me about about underwater basket weaving. But 1. this doesn't mean under water basket weaving is not worth paying for BY THOSE PEOPLE WHO WANT TO LEARN THIS SKILL, nor 2. that just because there are other underwater basket weaving experts out there, that i can't find a small niche of people to teach them what i know about underwater basket weaving.

I am not an underwater basket weaver. But my point is: Just because YOU wouldn't pay for X, doesn't mean X isn't valuable enough to pay for to others. Your goal, no matter your idea, is to find where these people are and show them your finished product. Some of them will buy. If enough don't to replace your income, move on to the next idea. Ideas are a dime a dozen.

Maybe i just have TOO many ideas. Maybe i just have too many BAD ideas. But ideas have never been my problem. EXECUTION is my problem. Which leads to...

2. This can be difficult. When you come up with an idea, you'll get super excited, and have all the motivation in the world to work 10-, 12-, 24-hour stretches, no matter what constraints you have...for the first couple days. Then you'll lose that motivation and will have to rely on DISCIPLINE and HABITS. Motivation is overrated. No matter how motivated you WANT to be, life destroys your motivation: You'll get tired, stuck in the code, bored with non-cool parts of the app, family responsibilities will take priority, your friends will want to hangout, etc. This is when you need to be DISCIPLINED and hopefully have good time management HABITS. I lack both of these integral skills :(

However, they are also simple to build...over time.

You say you don't feel like working on side-projects after working 9-5. Well most of us don't want to either. But the alternative is sticking with the 9-5 grind. If you're like me, that terrifies the F out of you. I'm 42, have a great family, a good 9-5, but everyday of my life i think only of leaving my 9-5. Maybe this is the source of my motivation - i want the freedom to work on what i want when i want, and in this day and age, it has never been easier to do so.

I built out a blog site to make myself accountable and publicly track the progress of building my ideas. I let my bad habits (I hate you, procrastination!!!) and fears stop me from following through last year. I'm on a decent run building , but not publicly discussing/sharing, this year so far). To see what I'm building check it out here: https://solomaker.life/ (at the bottom: click 'Show Startups'). They may not all be the GREATEST or MOST UNIQUE ideas, but everyone of them COULD be monetized, and everyone of them solves some sort of problem i have in my daily life or have faced in my daily life. And by 'problem', i simply mean, 'some sort of task i needed to do that took longer than 15 minutes'. Doesn't matter if something similar already exists: i just want to carve out a small sliver of a small sliver of the global population online.

If the last thing you feel like doing after work is more work, then regardless of any ideas you might come up with, you are simply not ready to build side projects for profit. This is hard, lonely, and takes discipline , time management skills, good habits, and hard work. It doesn't have to for very long, but to get something built, launched, and grown, you've got to have the discipline to work on it when you don't want to work on it. Or just quit your job and work 9-5 on building a profitable start-up. Don't fall into the trap of 'I want the thing, but i don't want to put in the effort of making the thing, so I'm going to ask others how to get the thing, but not put in the necessary time to make the thing.'. Trust me, don't wasted 15 years wishing about it, when it's so simple to just make it happen. All you have to do is start right now.